1. Technical Field
The present invention relates to a metal-polishing liquid and a polishing process therewith, in more detail, a metal-polishing liquid used in a wiring process in semiconductor device production and a polishing process therewith.
2. Related Art
Recently, in the development of semiconductor devices typified by semiconductor integrated circuits (hereinafter, appropriately referred to as “LSI”), in order to achieve smaller size and higher speed, higher densification and higher integration by miniaturization of wirings and lamination are in demand. As a technique for this, various techniques such as chemical mechanical polishing (hereinafter, appropriately referred to as “CMP”) are in use. The CMP is a process that is used to polish metal thin films used in insulating thin films (SiO2) and wirings in the production of semiconductor devices to remove superfluous metal thin films when a substrate is smoothed and wirings are formed (see, for instance, U.S. Pat. No. 4,944,836).
The metal-polishing liquid used in the CMP generally includes abrasive grains (such as alumina) and an oxidizing agent (such as hydrogen peroxide). The mechanism of the polishing by means of the CMP is considered to be that the oxidizing agent oxidizes a metal surface and a film of the oxide is removed by the abrasive grains to carry out polishing (see, for instance, Journal of Electrochemical Society, Vol. 138(11), pages 3460 to 3464 (1991)).
However, when the CMP is applied by use of the metal-polishing liquid containing such solid abrasive grains, in some cases, polishing scratches, a phenomenon where an entire polishing surface is polished more than necessary (thinning), a phenomenon where a polished metal surface is not planar, that is, only a center portion is polished-deeper to form a dish-like concave (dishing), or a phenomenon where an insulating material between metal wirings is polished more than necessary and a plurality of wiring metal surfaces forms dish-like concaves (erosion) may be caused.
Furthermore, when the metal-polishing liquid containing solid abrasive grains is used, in a cleaning process that is usually applied to remove the polishing liquid remaining on a polished semiconductor surface, the cleaning process becomes complicated and, furthermore, in order to dispose of the liquid after the washing (waste liquid), the solid abrasive grains have to be sedimented and separated; accordingly, there is a problem from the viewpoint of cost.
In order to overcome such problems of the conventional abrasive grains, for instance, a metal surface polishing process where a polishing liquid that does not contain abrasive grains and dry etching are combined is disclosed (see, for instance, Journal of Electrochemical Society, Vol. 147 (10), pages 3907 to 3913 (2000)). Furthermore, as a metal-polishing liquid that does not contain abrasive grains, a metal-polishing liquid that is made of hydrogen peroxide/malic acid/benzotriazole/ammonium polyacrylate and water, and a polishing process therewith are disclosed (see, for instance, Japanese Patent Application Laid-Open (JP-A) No. 2001-127019). According to the polishing processes described in these documents, a metal film of a convex portion of a semiconductor substrate is selectively subjected to the CMP and a metal film of a concave portion is left to form a desired conductor pattern. However, since the CMP advances due to friction with a polishing pad that is mechanically far softer than a conventional one that contains abrasive grains, there is a problem in that a sufficient polishing speed is difficult to obtain.
As wiring metals, so far, tungsten and aluminum have been generally used in the interconnect structure. However, in order to achieve higher performance, LSIs that use copper which is lower in wiring resistance than these metals have been developed. As a process for wiring copper, for instance, a damascene process disclosed in JP-A No. 2-278822 is known. Furthermore, a dual damascene process where a contact hole and a wiring groove are simultaneously formed in an interlayer insulating film and a metal is buried in both is in wide use. As a target material for such copper wiring, a copper target having high purity of five ninths or more has been used. However, recently, as the wirings are miniaturized to carry out further densification, the conductivity and electric characteristics of the copper wiring require improvement; accordingly, a copper alloy where a third component is added to high-purity copper is under study. Simultaneously, a high-performance metal-polishing means that can exert high productivity without contaminating the high-precision and high-purity material is in demand.
Furthermore, recently, in order to improve the productivity, a wafer diameter when LSIs are produced is enlarged. At present, a diameter of 200 mm or more is generally used, and production at a magnitude of 300 mm or more as well has been started. As the wafer diameter is made larger like this, a difference in polishing speeds at a center portion and a periphery portion of the wafer tends to occur; accordingly, achievement of uniformity in the polishing is becoming important.
As a chemical polishing process that does not apply mechanical polishing means to copper and a copper alloy, a process that makes use of a chemical solvent action is known (see, for instance, JP-A No. 49-122432). However, in the chemical polishing process that depends only on the chemical solvent action, in comparison with the CMP where a metal film of a convex portion is selectively chemomechanically polished, a concave portion is polished, that is, dishing is caused; accordingly, a large problem remains with respect to the planarity.
Furthermore, an aqueous dispersion element for chemical mechanical polishing, which contains an organic compound that inhibits the polishing pad from deteriorating, is disclosed (see, for instance, JP-A No. 2001-279231). However, even when the polishing aqueous dispersion element is used, there remains a concern in that the dishing phenomenon where a metal of a wiring portion is excessively polished to hollow out like a dish may be caused.
Other than the above, in order to planarize a polished surface, a working liquid that contains a chelating agent selected from iminodiacetate useful for correcting a wafer surface and salts thereof (see, for instance, Japanese Patent Application National Phase Publication No. 2002-538284) and a chemical mechanical polishing composition containing α-amino acid (see, for instance, JP-A No. 2003-507894) are proposed. Owing to these technologies, the polishing performance in the copper wiring may be improved.
Furthermore, usually, after the copper wiring is subjected to high-performance polishing, tantalum or a tantalum alloy that is frequently used as a barrier metal of the copper wiring and copper are precisely polished to planarize the vicinity of the wiring. Accordingly, realization of a polishing liquid that has, at the end of the copper polishing, polishing selectivity between copper and tantalum (hereinafter, appropriately referred to as “copper/tantalum polishing selectivity”) in which copper is readily ground and tantalum is difficult to grind is desired.